Apparatus and method for gating transmission of a data rate control channel in an HDR mobile communication system

ABSTRACT

A communication method in a mobile communication system in which an access terminal transmits to an access network DRC information indicating a selected one of forward data rates requested by the access terminal is provided. The access network designates a DRC information length DRC Length indicating a number of slots where the DRC information is repeated and transmits the designated DRC information length to the access terminal. The access terminal gates transmission of DRC information to the access terminal at one time slot in every DRC information length received from the access network.

PRIORITY

This application claims priority to an application entitled “Apparatusand Method for Gating Transmitting Data Rate Control Channel in an HDRMobile Communication System” filed in the Korean Industrial PropertyOffice on Jun. 21, 2000 and assigned No. 2000-34335, an applicationentitled “Apparatus and Method for Gating Data Rate Control Channel inan HDR Mobile Communication System” filed in the Korean IndustrialProperty Office on Jun. 27, 2000 and assigned No. 2000-37457, anapplication entitled “Apparatus and Method for Gating Data Rate ControlChannel in an HDR Mobile Communication System” filed in the KoreanIndustrial Property Office on Jul. 4, 2000 and assigned No. 2000-38084,and an application entitled “Apparatus and Method for Gating Data RateControl Channel in an HDR Mobile Communication System” filed in theKorean Industrial Property Office on Jul. 27, 2000 and assigned No.2000-45394, the contents of each of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method fortransmitting a data rate control (DRC) channel in a mobile communicationsystem employing a high data rate (HDR) technique, and in particular, toan apparatus and method for gating or repeating transmission of a DRCchannel.

2. Description of the Related Art

In an IS-2000 communication system, in a good channel state, a basestation and a mobile station perform power control in order to performcommunication at a prescribed data rate. On the other hand, in an HI)Rmobile communication system, access terminals (corresponding to themobile stations in the IS-2000 system) transmit DRC to an access network(corresponding to the base station in the IS-2000 system) at intervalsof a predetermined number of slots, and the access network then analyzesthe DRCs received from the access terminals and selectively transmitsdata only to the access terminals in a good channel state aftercontrolling a data rate. The HDR system has a forward link with highlyincreased throughput, so that it transmits a large amount of data perunit time in a good channel state and transmits a small amount of dataper unit time in a bad channel state, by varying a length of a packetusing a single common data channel within the limit of the maximum powerof the access network. That is, the HDR system transmits data to onlyone of the access terminals within a concerned access network at acertain time, through a common data channel. The HDR mobilecommunication system transmits channel state information and data ratecontrol (DRC) information using a DRC channel. Regarding the DRC, theaccess terminal measures a carrier-to-interference ratio (C/I) of apilot signal transmitted over a forward link creates the DRC based onthe measured C/I, and then reports the created DRC to the access networkover the DRC channel.

The pilot signal is used for initial sync acquisition of datatransmitted from the access terminal to the access network, for channelrecovery, and for indicating reverse power control information.Meanwhile, a reverse data rate indicator (RRI), used in the HDR system,is a signal for indicating a data rate of a reverse link andsynchronizing (or time-aligning) frames each comprised of 16 slots. TheDRC and the pilot signal are transmitted on a time division multiplexing(TDM) basis. Further, the RRI signal provides an index inserted in apunctured part of an encoded packet of the pilot signal, so as to helpthe access network to determine a data rate. Table 1 below shows reversedata rate indexes according to reverse data rates.

TABLE 1 Data Rate (Kbps) 4.8 9.6 19.2 38.4 76.8 153.6 Reverse Data Rate1 2 3 4 5 6 Indexes

In Table 1, when the reverse link is transmitted at a data rate of 153.6Kbsp, a 3-bit symbol is transmitted to the access network over a datarate index channel through Walsh symbol repetition using an orthogonalcode of length 4. Table 2 below shows an encoding table of the DRCchannel.

TABLE 2 Required Data Rate (Kbps) 4-bit DRC Codeword (8, 4, 4)  38.40000 00000000  76.8 0001 11111111  102.4 0010 01010101 153.6 (short)0011 10101010  204.8 0100 00110011 307.2 (short) 0101 11001100  614.40110 01100110  921.6 0111 10011001 1228.8 1000 00001111 1843.2 100111110000 2457.6 1010 01011010 Reserved 1011 10100101 153.6 (long) 110000111100 307.2 (long) 1101 11000011 Reserved 1110 01101001 Null rate1111 10010110

The access terminal measures a C/I of a signal transmitted from theaccess network, converts the measured C/I into a codeword associatedwith the data rate required by the access network in accordance withTable 2, and then reports the results to the access network. As shown inTable 2, the DRC signal is comprised of a 4-bit symbol. The 4-bit symbolis converted into an 8-bit codeword by block coding. The codewords aremapped with the required data rates of the forward traffic channel on aone-to-one basis.

FIG. 1 illustrates a structure of a reverse link transmitter in a commonHDR mobile communication system. Referring to FIG. 1, a multiplier 102channel-spreads a pilot channel 101 by multiplying it by an orthogonalfunction W₀ ⁴ of length 4 at every slot, and outputs a 1024-chipnon-modulated signal having a value ‘0’. RRI 103 is provided to an 8-aryorthogonal modulator 105. The 8-ary orthogonal modulator 105 performs8-ary orthogonal modulation on the provided RRI and outputs a Walshsymbol. A Walsh symbol repeater 107 repeats the Walsh symbol output fromthe 8-ary orthogonal modulator 105, and provides its output to amultiplier 109. The multiplier 109 multiplies the Walsh symbol outputfrom the Walsh symbol repeater 107 by an orthogonal function W₀ ⁴ oflength 4 at every slot, and outputs 64 chips per slot. A (8,4,4) blockencoder 117 block-encodes an input DRC 115. A codeword repeater 119repeats the block-encoded DRC a predetermined number of times. Amultiplier 121 spreads the symbols output from the codeword repeater 119by multiplying them by an orthogonal function W₀ ² of length 2. A Walshcover generator 113 outputs an orthogonal function of length 8corresponding to an input DRC Walsh cover index 111. A multiplier 123multiplies an output of the multiplier 121 by an output of the Walshcover generator 113. A multiplier 125 multiplies data output from themultiplier 123 by an orthogonal function W₀ ⁴ of length 4. A timedivision multiplexer (TDM) 127 time-multiplexes the pilot channelsignal, the RRI channel signal and the DRC channel signal outputrespectively from the multipliers 102, 109 and 125, and provides itsoutput to a complex spreader 141 as an in-phase component. An encoder131 encodes an input traffic channel signal 129. A modulator 133performs BPSK (Binary Phase Shift Keying) modulation on the encodedtraffic data. An interleaver 135 interleaves the BPSK-modulated data. Adata channel gain controller 137 gain-controls the output of theinterleaver 135. A multiplier 139 channel-spreads the signal output fromthe data channel gain controller 137 by multiplying it by an orthogonalfunction W₂ ⁴ of length 4, and provides its output to the complexspreader 141 as a quadrature phase component. The complex spreader 141complex-spreads the in-phase component signal and the quadrature phasecomponent signal. A baseband filter 143 baseband-filters thecomplex-spread signal from the complex spreader 141.

As described above, the pilot channel signal, the RRI channel signal andthe DRC channel signal are transmitted to the access network after timemultiplexing.

FIG. 2 illustrates a method for transmitting a DRC channel in a generalHDR system. As illustrated, each frame is comprised of 16 slots eachhaving a length of 2048 chips (=1.66 msec). In each slot, the pilotchannel signal and the DRC channel signal are time-multiplexed in a unitof 46 chips, before transmission. Every user (regardless of to whichuser group it belongs) continuously transmits the time-multiplexedsignal of the pilot channel signal and the DRC channel signal. In thiscase, there occurs interference between the users.

That is, as stated above, the HDR system continuously transmits thepilot and the DRC to the access network while the data service isconnected. Meanwhile, for the high-speed data transmission, informationon the C/I and the DRC signal, transmitted over the reverse link, mustbe correct. However, as shown in FIG. 2, since each user continuouslyreports the time-multiplexed signal of the pilot signal and the DRC tothe access network, there occurs interference between the pilots. If theaccess network fails to correctly detect the DRC, the access networkcannot correctly schedule the data rate and the sector required by theaccess terminal, so that it is not possible to service additional newusers. That is, in the conventional HDR system, when the number of usersis increased, it is difficult for the access network to detect the DRCcorrectly, making it impossible to service new users.

Although FIG. 2 shows a case where the pilot channel signal and the DRCchannel signal are subjected to time multiplexing, the same problem mayoccur even in the case where the pilot channel signal and the DRCchannel signal are subjected to code division multiplexing.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anapparatus and method for gating transmission of a DRC channel to preventinterference between DRC channels in an HDR mobile communication system.

It is another object of the present invention to provide an apparatusand method for transmitting a DRC channel at transmission power lowerthan that of a pilot channel by repeating the DRC channel, in order toprevent interference between DRC channels in an HDR mobile communicationsystem.

It is further another object of the present invention to provide anapparatus and method for determining a slotting rate at which an accessterminal gates transmission of a DRC channel by inverting a DRCinformation length in a mobile communication system, wherein an accessnetwork transmits the DRC information length indicating a frequency ofrepeating DRC, information at a plurality of time lots, to the accessterminal during call setup.

To achieve the above and other objects, there is provided acommunication method in a mobile communication system in which an accessterminal transmits to an access network (DRC information) indicating aselected one of forward data rates requested by the access terminal. Theaccess network designates a DRC information length (DRCLength)indicating a number of slots where the DRC information is repeated andtransmits the designated DRC information length to the access terminal.The access terminal gates transmission of DRC information to the accessterminal at one time slot in every DRC information length received fromthe access network.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram illustrating a structure of a reverse link in ageneral HDR mobile communication system;

FIG. 2 is a diagram illustrating a method for transmitting a DRC channelin the general HDR mobile communication system;

FIG. 3 is a diagram illustrating how an access network applies a datarate required by an access terminal to transmission data based on a DRCchannel received from the access terminal in the general HDR mobilecommunication system;

FIG. 4 is a diagram illustrating a structure of a reverse linktransmitter for transmitting a DRC channel in an HDR mobilecommunication system according to an embodiment of the presentinvention;

FIG. 5 is a diagram illustrating an operation of gating transmission ofa DRC channel to the access network and applying an offset to userpilots before transmission in the HDR mobile communication systemaccording to an embodiment of the present invention;

FIG. 6 is a diagram illustrating an operation of gating transmission ofa DRC channel to the access network and applying no offset to userpilots before transmission in the HDR mobile communication systemaccording to an embodiment of the present invention;

FIG. 7 is a diagram illustrating a method for transmitting DRC channelsdivided into 4 user groups and pilot signals having an offset in the HDRmobile communication system according to an embodiment of the presentinvention;

FIG. 8 is a diagram illustrating a method for transmitting DRC channelsdivided into 4 user groups and pilot signals having no offset in the HDRmobile communication system according to an embodiment of the presentinvention;

FIG. 9 is a diagram illustrating an example of an access networkreceiver in the HDR mobile communication system according to anembodiment of the present invention;

FIG. 10 is a diagram illustrating another example of an access networkreceiver in the HDR mobile communication system according to anembodiment of the present invention;

FIG. 11 is a flow chart illustrating a method for gating transmission ofa DRC channel based on a received

$\frac{E_{b}}{N_{t_{measure}}}$value in the access network of the HDR mobile communication systemaccording to an embodiment of the present invention;

FIG. 12 is a flow chart illustrating a method for switching from a gatedDRC transmission mode of a reverse link to a continuous transmissionmode in the access terminal of the HDR mobile communication systemaccording to an embodiment of the present invention;

FIG. 13 is a diagram illustrating a boundary value between a measured

$\frac{E_{b}}{N_{t_{measure}}}$value and a

$\frac{E_{b}}{N_{t_{measure}}}$value for determining a DRC channel symbol error rate and a transmissionmode in the access network of the HDR mobile communication systemaccording to an embodiment of the present invention;

FIG. 14 is a flow chart illustrating a method for gating transmission ofa DRC channel of a reverse link in the access terminal of the HDR mobilecommunication system according to an embodiment of the presentinvention;

FIG. 15 is a diagram illustrating a method for transmitting the same DRCchannel information over 4 consecutive slots at 25% of transmissionpower of the pilot in the HDR mobile communication system according toan embodiment of the present invention;

FIG. 16 is a diagram illustrating a case where one method fortransmitting the same DRC information over 4 consecutive slots attransmission power lower than that of the pilot and another method forgating transmission of the DRC information are simultaneously applied tothe HDR mobile communication system according to an embodiment of thepresent invention;

FIG. 17 is a diagram illustrating a structure of a reverse linktransmitter for transmitting a DRC channel in the HDR mobilecommunication system according to another embodiment of the presentinvention;

FIG. 18 is a flow chart illustrating a method for switching from theexisting continuous DRC transmission mode to a transmission mode fortransmitting the same DRC channel information over at least 2consecutive slots at transmission power lower than that of the pilotwhen a value calculated by the access network by measuring a signaltransmitted from each user exceeds a capacity of the reverse link;

FIG. 19 is a flow chart illustrating a procedure for transmitting asignaling message including slotting rate information in the accessnetwork in a gated DRC transmission mode according to an embodiment ofthe present invention;

FIG. 20 is a flow chart illustrating a procedure for determining a DRCinformation transmission start slot by receiving a signaling messageincluding the slotting rate information in the access terminal in thegated DRC transmission mode according to an embodiment of the presentinvention;

FIG. 21 is a diagram illustrating a DRC information application startpoint in the transmission method in which the slotting rate=¼ of theslotted transmission mode is applied in the case where the same DRC isrepeated 4 times (DRCLength=4) according to an embodiment of the presentinvention;

FIG. 22 is a diagram illustrating a DRC information application startpoint in a transmission method in which a slotting rate=½ of the slottedtransmission mode for the case where the same DRC information isrepeated 2 times (DRCLength=2) according to an embodiment of the presentinvention;

FIG. 23 is a diagram illustrating a DRC information application startpoint in which a slotting rate=¼ of the DRC transmission mode for thecase where the same DRC information is repeated 4 times (DRCLength=4)according to an embodiment of the present invention;

FIG. 24 is a diagram illustrating a method for transmitting DRC channelsdivided into 4 user groups in the case where the pilot and the DRCchannel are subjected to code division multiplexing in the HDR mobilecommunication system according to an embodiment of the presentinvention;

FIG. 25 is a diagram illustrating a structure of a reverse linktransmitter for transmitting a DRC channel, in the case where the pilotand the DRC channel are subjected to code division multiplexing in theHDR mobile communication system according to an embodiment of thepresent invention;

FIG. 26 is a diagram illustrating a structure of a forward linktransmitter in the HDR mobile communication system according to anembodiment of the present invention;

FIG. 27 is a flow chart illustrating a procedure for determining a datarate and an access terminal for receiving the forward channel describedin FIG. 28;

FIG. 28 is a diagram illustrating an interval for checking a forwarddata channel until the access terminal creates the next DRC informationafter reporting the DRC information to the access network; and

FIG. 29 is a flow chart illustrating a procedure for detecting forwardtraffic after transmitting the DRC information in the access terminalaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail since they would obscure the invention in unnecessary detail.

In the following description, the term “slotting rate (DRCSlotRate)”refers to a rate indicating at every how many slots the DRC channel istransmitted during gated transmission of the DRC channel. In addition,the term “user group” refers to a set of users that transmit the DRCchannel to the access network in the same slotting period, and have thesame DRC transmission start point within the frame. Here, not one butseveral users exist in each of the user groups.

Further, the term “repetition frequency (DRCLength)” refers to thefrequency of transmitting the same DRC channels, which indicates atevery how many slots the same DRC channel is repeated during repeatedtransmission of the same DRC channel. The slotting rate (DRCSlotRate) isdefined as a reciprocal of the repetition frequency (DRCLength)according to the present invention.

In addition, the term “continuous transmission mode” refers to a modewhere the user continuously transmits the DRC channel at every slot, andthe term “gated (or slotted) transmission mode” refers to a mode wherethe user periodically gates transmission of the DRC channel according tothe slotting rate (or gating rate) designated by the access network.Further, the term “repeated transmission mode” refers to a mode wherethe user repeatedly transmits the same DRC channel according to therepetition frequency DRCLength designated by the access network. Thepresent invention can switch from the continuous transmission mode tothe gated transmission mode, from the continuous transmission mode tothe repeated transmission mode and from the repeated transmission modeto the gated transmission mode, and vice versa.

FIG. 3 illustrates the timing for which an access terminal (AT) measuresa C/I of a signal transmitted from an access network (AN) and transmitsa DRC channel requiring a specific data rate to the access network, andthe access network then applies the data rate required by the accessterminal to transmission data based on the DRC channel received from theaccess terminal. In FIG. 3, the access network applies the required datarate through the DRC channel, a half slot after receiving the DRCchannel from the access terminal. Therefore, the HDR system schedulesthe user DRCs to be transmitted a half slot before one encoder packet isended, and provides a data service to the user in a good channel stateat the next encoder packet at the maximum power.

Now, a description will be made regarding a method for gatingtransmission of a DRC channel in order to reduce interference betweenuser DRCs when a capacity of the reverse link is exceeded, according toan embodiment of the present invention.

FIG. 4 illustrates a structure of a reverse link transmitter fortransmitting a DRC channel in an HDR mobile communication systemaccording to an embodiment of the present invention.

Referring to FIG. 4, a multiplier 102 orthogonal-spreads pilot channeldata 101 by multiplying it by a predetermined orthogonal code W₀ ⁴. Aswitch 401, under the control of a controller (not shown), switches theoutput of the multiplier 102 to a time division multiplexer (TDM) 127 ora 64-chip delay 403. The 64-chip delay 403 delays (or buffers) theoutput of the multiplier 102 for a predetermined time (e.g., 64-chipinterval) and provides its output to the multiplexer 127.

An 8-ary orthogonal modulator 105 performs 8-ary orthogonal modulationon an input reverse rate indicator (RRI) 103 and provides an outputsymbol. A Walsh symbol repeater 107 repeats the symbol output from the8-ary orthogonal modulator 105 a predetermined number of times. Amultiplier 109 orthogonal-spreads the output of the Walsh symbolrepeater 107 by multiplying it by the Walsh code W₀ ⁴.

A (8,4,4) block encoder 117 performs (8,4,4) block encoding on input4-bit DRC information 115. A codeword repeater 119 repeats the codewordoutput from the (8,4,4) block encoder 117 a predetermined number oftimes. A multiplier 121 orthogonal-spreads the output of the codewordrepeater 119 by multiplying it by a given Walsh code W₀ ² of length 2. AWalsh cover generator 113 outputs a Walsh cover for sector division byreceiving a DRC Walsh cover index. A multiplier 123 multiplies theoutput of the multiplier 121 by the output of the Walsh cover generator113. A switch 405, under the control of the controller, gates the outputof the multiplier 123. A multiplier 125 multiplies the output of theswitch 405 by the Walsh code W₀ ⁴. The multiplexer 127 time-multiplexesthe outputs of the multiplier 102 (or the delay 403), the multiplier 109and the multiplier 125.

An encoder 131 encodes input traffic data, and a modulator 133BPSK-modulates the output of the encoder 131. An interleaver 135interleaves the output of the modulator 133. A channel gain controller137 gain-controls the output of the interleaver 135. A multiplier 139multiplies the output of the channel gain controller 137 by apredetermined Walsh code W₂ ⁴ of length 4. A complex spreader 141complex-spreads the output (I-channel signal) of the multiplexer 127 andthe output (Q-channel signal) of the multiplier 139 by multiplying themby a predetermined PN (Pseudo Noise) code. A baseband filter 143baseband-filters the output of the complex spreader 141. The filteredsignal is converted into a radio frequency (RF) signal byfrequency-up-conversion, and then transmitted to the access network.

In the common HDR mobile communication system, the reverse link is suchstructured that each user should report the DRC to the access network atevery slot. In the present invention, when the capacity of the reverselink is exceeded (or saturated), the access terminal gates transmissionof the DRC to the access network. In order to gate transmission of theDRC to the access network, the access terminal must first knowinformation about a slotting rale, a slotting (or gating) start pointand a pilot offset. The information on the slotting rate, the slottingstart point and the pilot offset is transmitted directly or indirectlyfrom the access network to the access terminal through a signalingmessage. When the information is directly transmitted to the accessterminal, the information related to the slotting rate, the slottingstart point and the pilot offset, determined by the access network, istransmitted to the access terminal using the signaling message. When theinformation is indirectly transmitted to the access terminal, the accessnetwork transmits the slotting rate and a MAC (Media Access Control)index to the access terminal, and the access terminal then determinesthe slotting start point and the pilot offset using the information fromthe access network.

As illustrated in FIG. 4, each user transmits the DRC channel and thepilot channel based on the assigned slotting rate, the slotting startpoint and the pilot offset information. More specifically, in FIG. 4.,the channel-spread pilot and the channel-spread DRC are provided to apilot signal offset part and a DRC signal gating part, respectively. TheDRC signal gating part can be comprised of the switch 405, as shown inFIG. 4. The pilot signal offset part can be comprised of the switch 401and the 64-chip delay 403 for delaying the pilot signal for apredetermined chip interval, as shown in FIG. 4. The switch 401 and theswitch 405, under the control of the controller, control a transmissionstart point of the pilot signal and gate transmission of the DRC channelaccording to the information on the slotting rate, the slotting startpoint and the pilot offset, received from the access network, thereby tominimize interference between the DRC channels.

FIGS. 5 and 6 illustrate a method for continuously transmitting thepilot signal and gating transmission of the DRC channel according to anembodiment of the present invention. This method is divided into onemethod for transmitting the pilot signal with an offset and anothermethod for transmitting the pilot signal with no offset. In the formercase where the pilot signal has an offset, the users are grouped into aplurality of user groups and the DRC channels are gated such that theyshould be transmitted at different slots according to the user groups,as shown in FIG. 5. For example, a first user group UG_1 transmits theDRC channel at the first slot, and the second user group UG_2 transmitsthe DRC channel at the second slot. The DRC channels are transmitted atpredetermined intervals determined according to the slotting rate. Sincethe user groups have different pilot signal transmission start points,the transmission power is uniformly distributed at the slot where theDRC channel is gated. When a specific user group is given a 64-chippilot offset as shown in FIG. 5, it is possible to reduce interferencebetween pilot signals from the users that transmit only the pilot signalbut not the DRC channel.

FIG. 6 illustrates a method for gating transmission of a DRC channel andcontinuously transmitting a pilot signal with no offset. In this case,when the second user transmits the DRC channel, there occurs nointerference between the DRC channel and another user's DRC channel asin FIG. 5.

Although FIGS. 5 and 6 show a case where the pilot signal and the DRCchannel are subjected to time division multiplexing, the invention canalso be applied to another case where the pilot signal and the DRCchannel are subjected to code division multiplexing. That is, by gatingtransmission of the DRC channel, it is possible to reduce interferenceto the reverse link. When the pilot signal and the DRC channel aresubjected to code division multiplexing, no offset is given to thecontinuous pilot signals.

FIGS. 7 and 8 illustrate a method for gating transmission of the DRCchannel at a slotting rate DRCSlotRate=¼ according to an embodiment ofthe present invention. Specifically, FIG. 7 shows one case where anoffset is given to the pilot signals according to the user groups, andFIG. 8 shows another case where no offset is given to the pilot signals.When the slotting rate is ¼, the users are divided into 4 user groups.Each user is provided with the slotting rate ¼ and the slotting startpoint through a signaling message transmitted from the access network.

Referring to FIG. 7, the users in the first user group UG_1 are assignedthe slotting rate ¼ and the slotting start point (1^(st) slot) throughthe signaling message. Similarly, the users in the second user groupUG_2 are also assigned the slotting rate ¼ and the slotting start point(2^(nd) slot). In the same method, the users belonging to the third andfourth user groups UG_3 and UG_4 are also assigned the slotting rate ¼and the 3^(rd) and 4^(th) slots as their slotting start points. Theusers gate transmission of the DRC channels to the access network at thedesignated periods beginning at their slotting start points according tothe assigned slotting rate and slotting start points. In FIG. 3 above,the DRC is applied after a half slot. Therefore, if an encoded packet iscomprised of 4 slots as shown in FIG. 7, the DRC is applied only to thefirst user group UG_1. Specifically, regarding the DRC application pointof each user received at the access network, the DRIC transmitted a halfslot before one encoder packet is ended is applied. Therefore, when theslotting rate is ¼, only the first user group UG_1 transmits the DRC, ahalf slot before one encoder packet is ended. That is, the DRC appliedto the data transmitted from the access network becomes the DRCtransmitted by the first user group UG_1. Therefore, in order for theaccess network to schedule the DRC at every slot, it is preferable todetermine a data rate of the forward link in consideration of the DRC ofthe user group applied at the corresponding slot and the latest DRCinformation of the previous user group during a period corresponding tothe slotting rate before the corresponding slot.

Although FIG. 7 shows a case where the pilot signal and the DRC channelare subjected to time division multiplexing, the gated transmission canalso be equally applied to another case where the pilot signal and theDRC channel are subjected to code division multiplexing. By gatingtransmission of the DRC channel, it is possible to reduce interferenceto the reverse link.

FIG. 8 illustrates a method for gating transmission of the DRC channelsat a given slotting rate beginning at a given slotting start pointaccording to the user groups and continuously transmitting the pilotsignals with no offset, as described with reference to FIG. 7. When anoffset is given to the pilot signal as shown in FIGS. 5 and 7, thereoccurs no interference with the pilot signals from the users in theother user groups. However, there exists interference with the userstransmitting the DRC channels. When no offset is given to the pilotsignal, the performance is the same as in the conventional HDR systemexcept for the case where transmitting the DRC is gated. In this case,interference between the pilot signals may increase compared with thecase where an offset is given to the pilot signals, but the interferencemay be reduced in an interval where the DRC is transmitted.

Although FIG. 8 shows a case where the pilot signal and the DRC channelare subjected to time division multiplexing, the gated transmission canalso be equally applied to another case where the pilot signal and theDRC channel are subjected to code division multiplexing. By gatingtransmission of the DRC channel, it is possible to reduce interferenceto the reverse link.

In the gated DRC transmission method proposed by the present invention,when the capacity of the reverse link is exceeded (or saturated), eachuser gates transmission of the DRC channel, thereby to decreaseinterference between users and also decrease the capacity of the reverselink.

In the conventional HDR system, each access terminal (AT) transmits theDRC at every slot, as mentioned above, and the capacity of the reverselink is restricted. Therefore, if the number of users for the reverselink exceeds the capacity, a new access terminal (AT) cannot receivedata over the forward link. Therefore, the access terminal (AT) mustincrease the capacity of the reverse link by switching from thecontinuous DRC transmission mode to the gated (or slotted) DRCtransmission mode.

When the capacity of the reverse link exceeds a predetermined referencevalue, the access network (AN) must determine a ratio of a DRC powervalue to interference by the other access terminals (ATs). A thresholdvalue for an error rate per frame of the DRC channel is defined asDRC_(SER) and a signal-to-noise ratio corresponding to the thresholdvalue DRC_(SER) is defined as E_(b)/N_(t) _(Thresh) . Further, receptionpower of the access network (AN) before despreading by each accessterminal (AT) is defined as P_(u) _(i) (i=1, . . . , N), the sum ofreceived signal powers including noises before despreading by eachaccess terminal (AT) is defined as I_(o), and DRC power at the receiverof a certain access terminal (AT) is defined as

E_(DRC^(U_(i_(R_(x))))).Therefore, in the process of detecting the DRC for the first user, theinterference is represented by I_(o)−P_(u) _(i) . Therefore, a ratio ofthe DRC reception power

E_(DRC^(U_(i_(R_(x)))))to a value determined by subtracting the signal power P_(u) _(i) fromthe interference I_(o), including the noises, of the other accessterminals is represented by Equation (1) below. Equation (1) representsa ratio of DRC power to total interference of a certain user.

$\begin{matrix}{{\frac{E_{{DRC}^{U_{1}}}}{N_{t}} = {{\frac{E_{{DRC}_{R_{x}}^{0}}}{I_{o} - P_{u_{i}}}\mspace{14mu} i} = 1}},\ldots\;,N} & (1)\end{matrix}$

A method for determining a value for switching from the continuous DRCtransmission mode to the gated DRC transmission mode, i.e., a standardsignal-to-noise ratio E_(b)/N_(t) _(measure) of a DRC signal usingEquation (1), is divided into two methods: a first method defines anaverage ratio of the DRC reception power of each user to interferencewith other users as E_(b)/N_(t) _(measure) , and a second method definesthe minimum ratio of the DRC reception power of each user tointerference with other users as E_(b)/N_(t) _(measure) .

FIGS. 9 and 10 illustrate a structure of a reverse link receiver fordetermining the value E_(b)/N_(t) _(measure) so as to switch to thegated DRC transmission mode when the capacity of the reverse linkexceeds a predetermined reference value according to an embodiment ofthe present invention. Since every user has the same receiver structure,only the structure of the first user's receiver will be described belowwith reference to FIGS. 9 and 10.

The first method will be described with reference to FIG. 9. The accessnetwork receiver measures signal power P_(u) _(i) received from thefirst user USER1 of the first access terminal AT1, using an I squarer1001, a Q squarer 1003 and a summer 1005. In the same manner, the signalpower P_(u) _(N) from the other users is measured through the associatedI squarer and Q squarer. The measured signal power is provided to asummer 1007 which measures the I_(o) value by summing up the signalpower from all users. A subtracter 1023 subtracts the P_(u) ₁ from theI_(o), thereby obtaining the value I_(o)−P_(u) ₁ equivalent to a valuedetermined by subtracting its signal power from the signal power of allusers. The I squarer 1001, the Q squarer 1003, the summer 1005, thesummer 1007 and the subtracter 1023 constitute a “power measurementpart” for measuring interference between the access terminal and theother access terminals. In addition, the I and Q signals from the firstuser USER1 are provided to a complex despreader 1009 for complexdespreading. A multiplier 1011 channel-despreads the complex-despread Isignal by an orthogonal function W ⁰ ⁴ of length 4, and a multiplier1013 channel-despreads the complex-despread Q signal by an orthogonalfunction W ² ⁴ of length 4. The channel-despread I signal has the pilotsignal, the DRC and the RRI. A DRC extractor 1015 extracts the DRC fromthe channel-despread I signal and provides the extracted DRC to adecoder 1019. The decoder 1019 decodes the DRC into the original DRC. Adecoder 1017 decodes the channel-despread Q signal and outputs trafficdata. A DRC measurer 1021 measures reception power E_(DRC) _(u) _(i) ofthe DRC provided from the decoder 1019. A DRC E_(b)/N_(t) measurer 1025calculates a DRC E_(b)/N_(t) for the first user USER1 by receiving theoutput value Io−P_(u) ₁ of the subtracter 1023 and the output valueE_(DRC) _(u) _(i) of the DRC measurer 1021. An average DRC E_(b)/N_(t)measurement part for measuring an average E_(b)/N_(t) (signal-to-noiseratio) of the DRC channels by receiving the signal-to-noise ratios ofthe DRC channels from all the users is comprised of a summer 1029 and amultiplier 1031 as shown in FIG. 9. The summer 1029 sums up E_(b)/N_(t)of the DRC channels from the respective users, and the multiplier 1031divides the summed signal by the number N of the users and outputs anaverage E_(b)/N_(t) of the DRC channels. A controller 1035 compares theaverage E_(b)/N_(t) of the DRC channels, output from the multiplier1031, with a predetermined reference value in order to determine whetherto gate the DRC channel and also to determine a corresponding slottingrate.

Next, the second method will be described below with reference to FIG.10. The first method of FIG. 9 calculates the DRC E_(b)/N_(t) (or DRCreception power) by averaging DRC E_(b)/N_(t) values of the respectiveusers, whereas the average DRC E_(b)/N_(t) measurement part in thesecond method of FIG. 10 is comprised of a minimum value detector (MIN)1101. The minimum value detector 1101 receives the DRC E_(b)/N_(t)values of the respective users and outputs the minimum DRC E_(b)/N_(t)value as E_(b)/N_(t) _(measure) . The controller 1035 then compares theminimum DRC E_(b)/N_(t) output from the minimum value detector 1101 withthe predetermined reference value to determine whether to gate the DRCchannel and also to determine a corresponding slotting rate.

That is, the E_(b)/N_(t) _(measure) value calculated by the method ofFIG. 9 or 10 is provided to the controller 1035. The controller 1035performs an operation of a slotting rate determining algorithm of FIG.11 by receiving the E_(b)/N_(t) _(measure) value.

FIG. 11 illustrates a procedure for determining a slotting rate of theDRC channel by measuring strength of a signal received from each user inthe access network according to an embodiment of the present invention.Referring to FIG. 11, the controller 1035 of the access network (AN)receives the standard signal-to-noise ratio E_(b)/N_(t) _(measure) ofthe DRC channel, calculated in FIG. 9 or 10. Thereafter, in step 1101,the controller 1035 compares the standard signal-to-noise ratioE_(b)/N_(t) _(measure) of the DRC channel with E_(b)/N_(t) _(Thresh) +Δ.If E_(b)/N_(t) _(measure) is larger than E_(b)/N_(t) _(Thresh) +Δ, thecontroller 1035 proceeds to step 1111, and otherwise, proceeds to step1103. In step 1103, the controller 1035 compares E_(b)/N_(t) _(measure)with E_(b)/N_(t) _(Thresh) −δ₂. If E_(b)/N_(t) _(measure) is larger thanE_(b)/N_(t) _(Thresh) −δ₂, the controller 1035 sets the slotting rate to½ in step 1107. Otherwise, the controller 1035 proceeds to step 1105. Instep 1105, the controller 1035 determines whether E_(b)/N_(t) _(measure)is larger than E_(b)/N_(t) _(Thresh) −δ₃. If E_(b)/N_(t) _(measure) islarger than E_(b)/N_(t) _(Thresh) −δ₃, the controller 1035 sets theslotting rate to ¼ in step 1109. If the condition of step 1105 is notsatisfied, the controller 1035 repeatedly performs the same processwhile changing the error margin Δ. Herein, since one frame is comprisedof 16 slots, the slotting rate can be set up to 1/16. For example,regarding a unit of data transmitted from the access terminal to theaccess network, the data is transmitted in a unit of encoder packetcomprised of 32 slots. Since the access network is frame-synchronizedwith the access terminal, the possible maximum slotting rate is 1/16,and the slotting start point can also become one of 16 positions.

Δ, δ₂ and δ₃ indicate error margins. After determining the slotting ratethrough the above process, the controller 1035 determines in step 1111the slotting rate, the slotting start point and the pilot offset foreach access terminal using the reverse link data rate and slotting rateinformation received from the access terminal (AT). Further, thecontroller 1035 groups the DRCs of the reverse link according to thedetermined slotting rate. In step 1113, the controller 1035 creates asignaling message including the slotting rate, the slotting start pointand the pilot offset, and transmits the created signaling message to therespective access terminals (ATs) After transmitting the signalingmessage, the controller 1035 performs the above process again for thenext slot in step 1115.

The signaling message has the following format. For example, thesignaling message is realized using a reserved field of the existingtraffic channel assignment message. That is, it is possible either torealize a DRC slotting control message using the previously definedmessage or to define a new message. The traffic channel assignmentmessage has a format shown in Table 3 below.

TABLE 3 Field Length (bits) MessageID 8 MessageSequence 8ChannelIncluded 1 Channel 0 or 32 RABLength 2 DRCLength 2 NumPilots 4PilotPN 9 SoftHandoff 1 MacIndex 5 DRCCover 3 DRCSlotMode 1 DRCSlotRate2 DRCStarting_Point 4 Pilot_OFFset 1

In the conventional traffic channel assignment message format of Table3, the slotted DRC transmission mode field DRCSlotMode, the slottingrate field DRCSlotRate, the DRC slotting start point fieldDRCStarting_Point and the pilot offset field Pilot_OFFset are added forthe slotted DRC transmission. Each field will be described below indetail.

DRCSlotMode field records whether to gate the reverse DRC channel.

-   -   DRCSlotMode=‘0’ indicates the continuous DRC transmission mode    -   DRCSlotMode=‘1’ indicates the slotted DRC transmission mode

DRCSlotRate field records a slotting rate of the reverse DRC channel.

-   -   DRCSlotRate=‘00’ indicates a ½ slotting rate    -   DRCSlotRate=‘01’ indicates a ¼ slotting rate    -   DRCSlotRate=‘10’ indicates a ⅛ slotting rate    -   DRCSlotRate=‘1’ indicates a 1/16 slotting rate

DRCStarting_Point field records a start slot where the DRC channel isfirst transmitted when the reverse DRC channel is subjected to slottedtransmission.

-   -   DRCStarting_Point=‘0000’ indicates the 1^(st) slot    -   DRCStarting_Point=‘0001’ indicates the 2^(nd) slot    -   DRCStarting_Point=‘0010’ indicates the 3^(rd) slot

● ●

-   -   DRCStarting_Point=‘1110’ indicates the 15^(th) slot    -   DRCStarting_Point=‘1111’ indicates the 16^(th) slot

Pilot_OFFset field records whether to apply an offset when transmittingthe reverse pilot signal.

-   -   Pilot_OFFset=‘0’ indicates that no offset is applied.    -   Pilot_OFFset=‘1’ indicates that an offset is applied.

Table 4 below shows the fields added for DRC slotting control in theexisting channel assignment message. As shown in Table 4, it is alsopossible to transmit only the fields for DRC slotting control throughthe channel assignment message. That is, Table 4 shows a message formatused when transmitting only the DRC slotting control message instead ofretransmitting the channel assignment message. In Table 4, the MessageIDfield is used to identify the DRC slotting control message.

TABLE 4 Field Length (bits) MessageID 8 MessageSequence 8 DRCSlotMode 1RCSlotRate 2 RCStarting_Point 4 Pilot_OFFset 1

The signaling messages of Tables 3 and 4 transmit DRCSlotMode=‘0’ forthe continuous DRC transmission mode, and DRCSlotMode=‘1’ to switch tothe slotted DRC transmission mode. In order to provide a service to anew subscriber, the DRCSlotMode field is set to ‘1’.

FIG. 12 illustrates a procedure for switching from the slotted DRCtransmission mode of the reverse link to the continuous DRC transmissionmode when the capacity of the reverse link is improved because of adecrease in the number of users, according to an embodiment of thepresent invention.

Referring to FIG. 12, the controller 1035 determines in step 1201whether a condition of

$\frac{E_{b}}{N_{t_{measure}}} > {\frac{E_{b}}{N_{t_{thresh}}} + \Delta + \delta_{1}}$is satisfied. If the condition is satisfied, the controller 1035switches from the slotted DRC transmission mode to the continuous DRCtransmission mode in step 1203. Here, “δ₁” indicates a margin of theboundary value where switching occurs from the slotted DRC transmissionmode to the continuous DRC transmission mode.

After switching from the slotted DRC transmission mode to the continuousDRC transmission mode in step 1203, the controller 1035 informs theaccess terminal (AT) of the switching to the continuous DRC transmissionmode through the channel assignment message of Table 3 or 4, in step1205. However, if the condition is not satisfied in step 1201, thecontroller 1035 determines in step 1207 whether a condition of

$\frac{E_{b}}{N_{t_{measure}}} > {\frac{E_{b}}{N_{t_{thresh}}} - \delta_{2} + {\delta_{1}\;\frac{E_{b}}{N_{t_{measure}}}}} > {\frac{E_{b}}{N_{t_{thresh}}} - \delta_{2}}$is satisfied. If the condition is satisfied, the controller 1035switches to a slotting rate=½ DRC transmission mode in step 1209.However, if the condition is not satisfied in step 1207, the controller1035 switches to a slotting rate=¼ DRC transmission mode in step 1213.After the mode switching, the controller 1305 informs the accessterminal of the switched transmission mode through the channelassignment message of Table 3 or 4 in step 1211. After steps 1205 and1211, the controller 1035 performs the same process again for the nextslot in step 1215. Meanwhile, upon receipt of the message of Table 3 or4, the access terminal performs the procedure of FIG. 14.

For a better understanding of the invention, the process for switchingfrom the continuous transmission mode to the slotted transmission modeand from the slotted transmission mode to the continuous transmissionmode will be described in detail with reference to FIG. 13.

FIG. 13 illustrates boundary values for switching from the continuousDRC transmission mode to the slotted DRC transmission mode due to adecrease in the capacity of the reverse link, or from the slotted DRCtransmission mode to the continuous DRC transmission mode due to animprovement in the capacity of the reverse link.

As illustrated, reference numeral 13-1 indicates variation of a DRCsymbol error value according to E_(b)/N_(t) _(measure) , and referencenumeral 13-3 indicates a boundary of E_(b)/N_(t) _(thresh) correspondingto a preferable symbol error rate DRC_(SER) at the access network.Reference numeral 13-2 indicates a boundary where the slotting rate ischanged from ¼ to ½, and the DRC reception power corresponding to thisboundary becomes E_(b)/N_(t) _(Thresh) −δ₂. For example, if theE_(b)/N_(t) _(measure) value measured at the access network is largerthan E_(b)/N_(t) _(Thresh) −δ₂, and smaller than E_(b)/N_(t) _(thresh) ,the slotting rate is set to ½. However, if the measured E_(b)/N_(t)_(measure) value is smaller than E_(b)/N_(t) _(Thresh) −δ₂, the slottingrate is set to ¼. In this manner, it is possible to change the slottingrate according to the measured capacity of the reverse link.

Further, reference numeral 13-4 indicates a boundary for switching fromthe continuous DRC transmission mode to the slotted DRC transmissionmode if the capacity of the reverse link is exceeded. Thesignal-to-noise ratio (or reception power) of the DRC channelcorresponding to this, boundary becomes E_(b)/N_(t) _(Thresh) +Δ. Thatis, if E_(b)/N_(t) _(measure) is smaller than E_(b)/N_(t) _(Thresh) +Δ,switching from the continuous DRC transmission to the slotted DRCtransmission mode takes place. In addition, reference numeral 13-5indicates a boundary for switching back to the continuous DRCtransmission mode if the capacity of the reverse link is less than areference value in the slotted DRC transmission mode. Thesignal-to-noise ratio of the DRC channel corresponding to this boundarybecomes E_(b)/N_(t) _(Thresh) +Δ+δ₁. In this case, if E_(b)/N_(t)_(measure) is larger than E_(b)/N_(t) _(Thresh) +Δ+δ₁, switching to thecontinuous DRC transmission mode takes place.

As mentioned above, switching from the continuous DRC transmission modeto the slotted DRC transmission mode happens at the point whereE_(b)/N_(t) _(measure) is smaller than E_(b)/N_(t) _(Thresh) +Δ.Further, in the slotted DRC transmission mode, if E_(b)/N_(t) _(measure)is larger than E_(b)/N_(t) _(Thresh) −δ₂ but smaller than E_(b)/N_(t)_(Thresh) +Δ, the slotting rate is set to ½; if E_(b)/N_(t) _(measure)is smaller than E_(b)/N_(t) _(Thresh) −δ₂+δ₁ E_(b)/N_(t) _(Thresh) −δ₂the slotting rate is set to ¼. Here, δ₂ indicates a margin for changingthe slotting rate to ¼.

In addition, the point where switching takes place from the slotted DRCtransmission mode back to the continuous DRC transmission mode becauseof an improvement in the capacity of the reverse link is as follows. Inthe case where E_(b)/N_(t) _(measure) has a margin δ₁ for increasing adata rate, if the number of the reverse link users is decreasedimproving the capacity of the reverse link while the user chooses theslotted transmission mode for the reverse link because E_(b)/N_(t)_(measure) is measured to be smaller than E_(b)/N_(t) _(Thresh) +Δ+δ₁,switching takes place back to the continuous transmission mode. In thiscase, if E_(b)/N_(t) _(measure) is larger than E_(b)/N_(t) _(Thresh)+Δ+δ₁, switching happens from the slotted DRC transmission mode to thecontinuous DRC transmission mode. Here, δ₁ indicates a margin of theboundary value where switching occurs from the slotted DRC transmissionmode to the continuous DRC transmission mode.

FIG. 14 illustrates a procedure for detecting a slotting rate of the DRCchannel by analyzing a signaling message from the access network in theaccess terminal according to an embodiment of the present invention.

Referring to FIG. 14, upon receipt of a signaling message from theaccess network (AN) in step 1401, the access terminal (AT) detects, instep 1403, the slotted DRC transmission mode DRCSlotMode, the slottingstart point DRCStarting_Point, the slotting rate DRCSlotRate and thepilot offset Pilot_OFFset from the received signaling message, ordetermines the slotting start point DRCStarting_Point and the pilotoffset Pilot_OFFset using the slotted DRC transmission mode DRCSlotMode,the MAC index MacIndex and the slotting rate DRCSlotRate included in thechannel assignment message. After detecting the above information, theaccess terminal (AT) further determines in step 1403 whether the DRCchannel is subjected to the slotted transmission (DRCSlotMode=1), basedon the slotted transmission mode information DRCSlotMode detected fromthe channel assignment message. If DRCSlotMode=1, the access terminal(AT) gates transmission of the DRC channel according to the detectedslotting start point and slotting rate in step 1405. Thereafter, theaccess terminal (AT) determines in step 1407 whether to transmit thepilot signal with an offset (Pilot_OFFset=1), based on the pilot offsetinformation Pilot_OFFset included in the channel assignment message. Ifthe pilot signal has an offset (i.e., Pilot_OFFset=1), the accessterminal (AT) transmits the pilot signal with an offset as shown inFIGS. 5 and 7, in step 1409. If DRCSlotMode≠1 in step 1403, or ifPilot_OFFset≠1 in step 1407 or after transmitting the pilot signal withan offset in step 1409, then the access terminal (AT) prepares tocontrol the next slot in step 1411

In the embodiment of the present invention, the reverse DRC channel isgated (or slotted) in order to improve DRC detection capability of theaccess network. As another method for reducing reverse interference dueto the DRC channel, the HDR system transmits the same DRC channels overat least 2 consecutive slots at transmission power lower than that ofthe pilot channel. Hereinafter, a case where transmission output of theDRC channel is low will be described in detail.

FIG. 15 illustrates a method for repeatedly transmitting the same DRCchannels in the HDR mobile communication system according to anembodiment of the present invention. As illustrated, the number ofrepeated slots is 4. Therefore, the access terminal (AT) transmits thesame DRC channels over 4 slots according to the number of repeatedslots, specified by the access network. At this moment, the DRC channelis transmitted at transmission power lower than that of the pilotsignal. That is, the same DRC channels are transmitted over the 4consecutive slots at 25% of the transmission power of the pilot channel,thereby reducing interference due to the DRC channel transmitted by theaccess terminals in the reverse link. The access network acquires oneDRC channel having the same power as that of the reverse pilot channelby accumulating the DRC channels received at the 4 slots. That is, theacquired DRC channel has enough power required for demodulation.

Although FIG. 15 shows a case where the same DRC channels aretransmitted at the 4 consecutive slots, the same method can also beapplied to another case where the same DRC channels are transmitted at apredetermined number of consecutive slots. For example, the number ofrepeated slots can be 1, 2 or 4, as shown in Table 5 below. In addition,information on the number of consecutive slots where the same DRCinformation is transmitted and information on the transmission power forthe DRC information are transmitted from the access network to theaccess terminal through the signaling message. Alternatively, the accessnetwork transmits information on the number of repeated slots, and theaccess terminal then determines the transmission power for the DRCinformation using the information received from the access network.

For example, if the repetition frequency of the same DRC channels is 4,the transmission power for each DRC channel is set to 25% of thetransmission power of the pilot channel as shown in Table 5.

TABLE 5 Number of Slots for Repeated DRC Tx Power Compared with PilotTransmission of Same DRC Info Tx Power 1 100% 2  50% 4  25%

The method for transmitting the same DRC channels at 2 or moreconsecutive slots at reduced transmission power can also be applied tothe slotted DRC transmission mode described in the embodiment of thepresent invention. In this case, one or more of the same DRC channelsare slotted, and transmission power for the non-slotted DRC channels isset to be equal to or lower than the transmission power for the pilotchannel.

FIG. 16 illustrates a method for slotting at least one of the same DRCchannels in the HDR mobile communication system which repeatedlytransmits the same DRC channels according to an embodiment of thepresent invention. As illustrated, the number of repeated slots is 4.Therefore, the access terminal (AT) transmits the same DRC channels fora 4-slot interval. In this case, the access terminal slots the DRCchannels at the even-numbered slots (i.e., 2^(nd) and 4^(th) slots), andtransmits only the pilot channels at the odd-numbered slots. Further,the transmission power for the DRC channels transmitted at theodd-numbered slots (i.e., 1^(st) and 3^(rd) slots) is adjusted to belower than the transmission power for the pilot channels. For example,the transmission power for the DRC channels is adjusted to 50% of thetransmission power for the pilot channels. That is, the DRC channels oftwo slots out of the 4 consecutive slots transmitting the same DRCchannels are slotted, and the DRC channels of the other two slots aretransmitted at the transmission power lower than that of the pilotchannels.

That is, in another embodiment of the present invention, when thecapacity of the reverse link is exceeded, the access terminal transmitsthe same DRC channels at two or more consecutive slots at transmissionpower lower than that of the pilot channel. In order to repeatedlytransmit the DRC channels to the access network, the access terminalshould first know the number of slots where the same DRC channels arerepeated, and the transmission power for the DRC channels. Informationon the number of slots where the same DRC channels are repeated andinformation on the transmission power for the DRC channels aretransmitted from the access network to the access terminal through thesignaling message. Alternatively, the access network transmitsinformation on the number of DRC-repeated slots, and the access terminalthen determines the transmission power for the DRC channels using theinformation provided from the access network.

FIG. 17 illustrates a structure of a reverse link transmitter accordingto an embodiment of the present invention. Specifically, FIG. 17illustrates an apparatus for decreasing transmission power of the DRCchannels below the transmission power of the pilot channels, whentransmitting the same DRC channels at two or more consecutive slots.

As illustrated, the transmitter of FIG. 17 is similar in structure tothe transmitter of FIG. 1, except for the structure of the DRC channeltransmitter. Therefore, reference will be made only to the DRC channeltransmitter in the following description.

A (8,4,4) block encoder 117 performs (8,4,4) block encoding on 4-bit DRCinformation. In this embodiment, the (8,4,4) block encoder 117repeatedly encodes the same 4-bit DRC information a predetermined numberof times under the control of the controller. A codeword repeater 119repeats a codeword output from the (8,4,4) block encoder 117 apredetermined number of times. A multiplier 121 orthogonal-spreads theoutput of the codeword repeater 119 by multiplying it by a given Walshcode W₀ ² of length 2. A Walsh cover generator 113 outputs a Walsh coverby receiving a DRC Walsh cover index. A multiplier 123 multiplies theoutput of the multiplier 121 by the output of the Walsh cover generator113. A DRC gain controller 1700 gain-controls the output of themultiplier 123. For example, when the same DRC channels are repeated 4times in a 4-slot interval, the DRC gain controller 1700 adjusts thetransmission power for the DRC channels to 25% of the transmission powerfor the pilot channel. A multiplier 125 multiplies the output of the DRCgain controller 1700 by a predetermined orthogonal code W₀ ⁴, andoutputs a DRC channel signal. In order to switch from the repeatedtransmission mode to the slotted transmission mode, i.e., in order tosupport a transmission method of FIG. 21 which will be described later,a gating device (switch 405 of FIG. 4) can be provided between the DRCgain controller 1700 and the multiplier 125. Upon receipt of an order toswitch from the current repeated transmission mode to the slottedtransmission mode from the access network, the access terminal slots atleast one of the repeated DRC channels by controlling the gating device.Further, the access terminal also readjusts a gain of the DRC channelsignal using the DRC gain controller 1700. That is, the access terminaladjusts the gain of the DRC channel signals, so that the transmissionpower determined by accumulating the same DRC channel signals at theaccess network should be equal to the transmission power of the pilotchannel.

As described above, each user transmits the DRC channels and the pilotsignals based on the information on the number of DRC-repeated slots andthe information on the transmission power for the DRC channels, that is,the information being provided from the access network. Thechannel-spread DRC channel signal is provided to the DRC gain controller1700. The DRC gain controller 1700 controls transmission power of theDRC channels based on the DRC information transmission power determineddepending upon the number of slots where the same DRC information isrepeated. By controlling the transmission power of the DRC channels inthis manner, it is possible to reduce interference between the DRCchannels from the users.

Even in the method for transmitting the same DRC channels at two or moreconsecutive slots at transmission power lower than that of the pilotchannel, it is possible to reduce interference between pilot signalsusing the pilot offset in the reverse link. In this case, whether to setthe pilot offset can be directly informed to the access terminal using apredetermined field of the signaling message, or can be indirectlydetermined at the access terminal using the MAC index assigned by theaccess network. For example, the pilot offset is set according towhether the MAC index is an even number or an odd number.

FIG. 18 illustrates a procedure for switching from the existingcontinuous DRC transmission mode to a transmission mode for transmittingthe same DRC channels over at least 2 consecutive slots at transmissionpower lower than that of the pilot channel, when a value calculated bythe access network by measuring a signal transmitted from each userexceeds a capacity of the reverse link according to an embodiment of thepresent invention.

Referring to FIG. 18, the access network (AN) compares the valueE_(b)/N_(t) _(measure) measured in FIG. 9 or 10 with E_(b)/N_(t)_(thresh) +Δ in step 1801. If E_(b)/N_(t) _(measure) is larger thanE_(b)/N_(t) _(Thresh) +Δ, the access network proceeds to step 1811, andotherwise, proceeds to step 1803. The access network comparesE_(b)/N_(t) _(measure) with E_(b)/N_(t) _(thresh) −δ₂ in step 1803. IfE_(b)/N_(t) _(measure) is larger than E_(b)/N_(t) _(thresh) −δ₂, theaccess network determines to repeatedly transmit the reverse DRCchannels two times at 50% transmission power of the pilot channel instep 1807, and then proceeds to step 1811. Otherwise, the access networkproceeds to step 1805. The access network compares E_(b)/N_(t)_(measure) with E_(b)/N_(t) _(thresh) −δ₃ in step 1805. If E_(b)/N_(t)_(measure) is larger than E_(b)/N_(t) _(thresh) −δ₃, the access networkdetermines to repeatedly transmit the DRC channels four times at 25%transmission power of the pilot channel in step 1809, and then proceedsto step 1811. That is, if the repetition frequency of the same DRC is N,the transmission power of the DRC channels becomes 1/N times thetransmission power of the pilot channel. Here, Δ, δ₂ and δ₃ indicateerror margins. After determining the repetition frequency of the DRCchannel and the transmission power in this manner, the access networkassigns a decoder according to the determined repetition frequency ofthe DRC channel and the determined transmission power in step 1811.Thereafter, in step 1813, the access network transmits to the accessterminal (AT) the signaling message including the determined DRCrepetition frequency and transmission power information. Subsequently,the access network collects the received DRC channels according to therepetition frequency and then determines reception power of the DRCchannels in step 1815.

In FIGS. 15 to 18, the DRC repetition frequency and the DRC transmissionpower are determined after measurement of interference to the reverselink. Alternatively, however, it is also possible to reduce interferenceto the reverse link by decreasing transmission power of the DRC channelsbelow the transmission power of the pilot channel, if the same DRCchannels are transmitted at the consecutive slots before application ofthe above method. That is, when the DRC repetition frequency DRCLengthis 2 or 4, it is possible to reduce interference to the reverse link bydecreasing the transmission power of the DRC channels below thetransmission power of the pilot channel. For example, before applicationof the method for transmitting the same DRC channels over at least 2consecutive slots at decreased DRC transmission power, if the same DRCchannels have been previously transmitted in an N-consecutive slotinterval, it is possible to reduce interference to the reverse link bydecreasing the transmission power of the DRC channels to 1/N times thetransmission power of the pilot channel. In other words, when the DRCchannels are repeatedly transmitted at the same transmission power asthat of the pilot channel, the transmission power of the DRC channelscan be adjusted to be lower than that of the pilot channel through thesignaling message during transmission. In addition, during repeated DRCtransmission, the access network can also send a slotted transmissionorder to the access terminal through the signaling message. For example,if the reverse interference increases to exceed a threshold value duringthe repeated DRC transmission, the access network may order the accessterminal to slot transmission of the DRC channels. In this case, theaccess terminal determines the slotting rate DRCSlotRate by invertingthe repetition frequency DRCLength of the DRC channel assigned by theaccess network during call setup. A method for controlling the slottedDRC transmission using the DRC repetition frequency DRCLength will bedescribed below.

FIG. 19 illustrates a procedure for informing the access terminal of aslotting rate through the signaling message in the access networkaccording to an embodiment of the present invention. Referring to FIG.19, the access network determines the DRC repetition frequency DRCLengthand also determines the slotting rate DRCSlotRate by inverting the DRCrepetition frequency DRCLength in step 1901. The slotting rateDRCSlotRate is equal to a reciprocal of the DRC repetition frequencyDRCLength. Table 6 below shows the slotting rates DRCSlotRate associatedwith the repetition frequencies DRCLength indicating the number of theslots where the same DRC information is repeatedly transmitted.

TABLE 6 DRCLength DRCSlotRate 1 1 2 1/2 4 1/4

Thereafter, in step 1903, the access network creates a signaling messageincluding the MAC index (MacIndex), the slotted transmission modeDRCSlotMode (continuous transmission mode or slotted transmission mode)and the slotting rate DRCSlotRate (or DRCLength) of the respectiveaccess terminals. In step 1905, the access network transmits the createdsignaling message to the access terminal.

FIG. 20 illustrates a procedure for determining the slotting rate andthe slotting start point for slotted transmission of the reverse DRCchannels using the information included in the received signalingmessage in the access terminal. The signaling message including the MACindex MacIndex and the DRC repetition frequency DRCLength is transmittedto the access terminal during an initial access to the system. Whilerepeatedly transmitting the DRC channels according to the DRC repetitionfrequency included in the signaling message, upon receipt of a slottedtransmission order from the access netwirk, the access terminal performsslotted DRC transmission according to the slotting rate DRCSlotRatedetermined by inverting the DRC repetition frequency DRCLength.

Referring to FIG. 20, the access terminal receives the signaling messageincluding the MAC index MacIndex and the DRC repetition frequencyDRCLength from the access network in step 2001. When receiving the DRCrepetition frequency DRCLength, the access terminal determines theslotting rate DRCSlotRate by inverting the DRC repetition frequencyDRCLength. However, when the slotting rate DRCSlotRate is received, theaccess terminal determines the DRC repetition frequency DRCLength byinverting the slotting rate DRCSlotRate. That is, the access network isrequired to provide the access terminal with any one of the slottingrate DRCSlotRate and the DRC repetition frequency DRCLength. Thereafter,in step 2003, the access terminal calculates a slotting period using thedetermined slotting rate DRCSlotRate. The slotting period is areciprocal of the slotting rate DRCSlotRate. Therefore, the DRCrepetition frequency has the same value as the slotting period. In step2005, the access terminal calculates an index value which is equivalentto a remainder obtained by dividing the assigned MAC index (or DRC coverindex) by the slotting period. The access terminal determines in step2007 whether the determined index value is ‘0’. If the index value is‘0’, the access terminal determines the slotting start pointDRCStarting_Point of the DRC channels undergoing the slottedtransmission as a starting slot of one frame in step 2009. Otherwise,the access terminal determines in step 2011 whether the index value is‘1’. If the index value is ‘1’, the access terminal determines theslotting start point DRCStarting_Point of the DRC channels undergoingthe slotted transmission as a second slot of one frame in step 2013.After repeating such a process, the access terminal determines in step2015 whether the index value is ‘N−2’. If the index value is ‘N−2’, theaccess terminal determines the slotting start point DRCStarting_Point ofthe DRC channels undergoing the slotted transmission as an (N−1)^(th)slot of one frame in step 2019. Otherwise, the access terminaldetermines the slotting start point as an N^(th) slot of one frame instep 2017. For example, when the slotting rate is ¼ (DRCSlotRate=¼), theslotting period becomes 4 (=1/DRCSlotRate), and when the access terminalis assigned an MAC index of 27, it starts to transmit the DRC channels,after a lapse of 3 slots from the starting point of one frame.

In FIGS. 19 and 20, the slotted transmission mode is applied to the casewhere the same DRC channels are repeatedly transmitted at two or moreconsecutive slots. However, even in the continuous DRC transmissionmode, the access network determines the slotting rate by measuringinterference of the reverse link through the processes of FIGS. 9 and 10and provides the determined slotting rate information to the accessterminal, and the access terminal then calculates the starting slot ofone frame for the slotted DRC transmission by performing the steps 2001to 2019 of FIG. 20.

Although FIG. 20 shows how the access terminal determines the startingslot of the DRC channel within one frame, it is also possible todetermine whether to set a pilot offset using the same method. In thiscase, an offset is set up to the pilot according to whether a remainderobtained by dividing the MAC index assigned to the access terminal bythe slotting period is an odd number or an even number. Besides, it isalso possible to decide whether to set up the pilot offset according towhether the remainder obtained by dividing the MAAC index assigned tothe access terminal by the slotting period is larger than a thresholdvalue. For example, for the slotting rate DRCSlotRate=¼, if theremainder is smaller than 2, the pilot offset is set up. Otherwise, ifthe remainder is larger than or equal to 2, the pilot offset is not setup.

Although the invention has been described with reference to anembodiment where the access terminal determines the DRC slotting startpoint DRCStarting_Point and whether to set up the pilot offsetPilot_OFFset using the DRC slotting rate DRCSlotRate and the MAC indexMacIndex, it is also possible for the access network to determine theDRC slotting rate and the MAC index and transmit them to the accessterminal using the signaling message. In this case, the access networkmeasures power levels of the interference signals generated by therespective user groups out of received reverse signals, determines theDRC transmission start point such that the DRC slotting start pointDRCStarting_Point and the MAC index MacIndex should belong to the usergroup generating the least interference power, and transmits thisinformation to the access terminal through the signaling message. Inthis case, whether to set up an offset to the pilot channel can bedetermined according to the DRC slotting start point DRCStarting_Pointor the user group to which the access terminal belongs. In addition tothe method where the access network determines the DRC transmissionstart slot DRCStarting_Point and the pilot offset Pilot_OFFset andtransmits them to the access terminal, the access network may alsocalculate the number of users in the received user groups and thentransmit the DRC transmission start slot and the pilot offset of theuser group having the least number of users to the access terminal.

FIG. 21 illustrates a DRC information application start point in thetransmission method in which the DRCLength=4 slotted transmission modeis applied according to an embodiment of the present invention. In thiscase, the DRC information is applied to the forward link, a half slotafter the DRC information of every user group is received at the accessnetwork. That is, the access network applies the DRC information to theforward link after receiving the DRC information belonging to every usergroup, transmitted in the same slotting interval (4 slots). AlthoughFIG. 21 shows a case where the access network applies the DRCinformation to the forward link after receiving the DRC information ofevery user group, transmitted in the same slotting interval (4 slots),the access network may also determine the data rate of the forward linkusing the last received DRC information of the respective user groupsbefore receiving the DRC information of every user group, transmitted inthe same slotting interval (4 slots).

Although FIG. 21 illustrates an application of the slotted transmissionmode for the case where the same DRC information is repeated 4 times(DRCLength=4), the slotted transmission mode can also be applied evenwhen the same DRC information is repeated N times. When the repetitionfrequency is DRCLength=N, the slotting rate becomes DRCSlotRate=1/N andthe access network applies the DRC information to the forward link afterreceiving the entire DRC information transmitted in the same slottinginterval (N slots). Even in this case, it is possible to reduceinterference to the reverse link by applying the pilot offset in thesame method.

FIG. 22 illustrates a DRC information application start point in thetransmission method to which a DRCLength=2 slitted transmission modeaccording to an embodiment of the present invention. In this case, theDRC information is applied to the forward link, a half slot after theDRC information of every user group is received at the access network.That is, the access network applies the DRC information to the forwardlink after receiving tie DRC information belonging to every user group,transmitted in the same slotting interval (2 slots). Although FIG. 22shows a case where the access network applies the DRC information to theforward link after receiving the DRC information of every user group,transmitted in the same slotting interval (2 slots), the access networkmay also determine the data rate of the forward link using the lastreceived DRC information of the respective user groups before receivingthe DRC information of every user group, transmitted in the sameslotting interval (2 slots).

FIG. 23 illustrates a method in which the access network receiverapplies the DRC information to the forward link at a given point in theslotting interval before receiving the DRC information of every usergroup corresponding to the same slotting interval (4 slots) according toan embodiment of the present invention. When the DRC channels aresubjected to the slotted transmission, the access network may receivethe DRC information or may not receive the DRC information at a certaintime point. For the non-received DRC information of the user group, theaccess network determines the data rate of the forward link using thelast received DRC information. In this state, the access network hasreceived only the DRC information from the first and second user groupsUG1 and UG2 in the access terminal's DRC slotting interval n+1, but hasnot received the DRC information from the third and fourth user groupsUG3 and UG4 in the slotting interval n+1. In this case, the accessnetwork determines the data rate of the forward link using the lastreceived DRC information, i.e., the DRC information in the slottinginterval n. That is, the access network selects the access terminalexpected to receive the forward data by comparing the DRC informationfrom the user groups UG3 and UG4, received in the n^(th) interval, withthe DRC information from the user groups UG1 and UG2, received in the(n+1)^(th) interval, and then transmits the data to the selected accessterminal at the determined data rate.

Although FIG. 23 shows a case where the access network fails to receivethe DRC information from the third and fourth user groups UG3 and UG4,the invention can also be equally applied to the case where the accessnetwork fails to receive the DRC information from other user groups. Inaddition, the invention can also be applied to the case where the numberof user groups is not 4.

While the invention has been described with reference to an embodimentwhere the pilot signals and the DRC channels are subjected to the timedivision multiplexing, the invention can also be applied to the casewhere the pilot signals and the DRC channels are subjected to the codedivision multiplexing.

FIG. 24 illustrates an example of the slotted transmission mode for thecase where the pilot signal and the DRC channel are subjected to codedivision multiplexing according to an embodiment of the presentinvention. Specifically, FIG. 24 illustrates a transmission method towhich the DRCSlotRate=¼ slotted transmission mode where the same DRCinformation is repeated 4 times (DRCLength=4). In this case, since thepilot signal and the DRC channel are subjected to code divisionmultiplexing, it is not necessary to allocate an offset to the pilotsignal. Therefore, when the slotted transmission mode is applied, theaccess terminal continuously transmits the DRC channels without timedivision multiplexing with the pilot channels, using all of the 2048chips at the slot assigned to the access terminal itself. Slotting whichone of the four slots having the same information is determined usingthe signaling message transmitted from the access network.

FIG. 25 illustrates a structure of a reverse link transmitter fortransmitting the pilot signal and the DRC channel on a code divisionmultiplexing basis according to an embodiment of the present invention.

Referring to FIG. 25, an orthogonal Walsh modulator 2601 performs n-aryorthogonal modulation on a reverse rate indicator (RRI) and outputs asymbol. A symbol repeater (or codeword repeater) 2602 repeats the symboloutput from the orthogonal Walsh modulator 2601 a predetermined numberof times. A time division multiplexer (TDM) 2603 time-multiplexes theoutput of the symbol repeater 2602 with pilot data of all 0's (or all1's) according to a predetermined rule. A signal point mapper 2604 mapsthe data output from the time division multiplexer 2603 into +1 or −1. Amultiplier 2605 orthogonal-spreads the output of the signal point mapper2604 by multiplying it by a predetermined Walsh code W₀ ¹⁶. A gaincontroller 2606, under the control of the controller, gain-controls theoutput of the multiplier 2605.

A biorthogonal encoder 2607 performs biorthogonal encoding on input DRCinformation. A codeword repeater 2608 repeats a codeword output from thebiorthogonal encoder 2607 a predetermined number of times. A signalpoint mapper 2609 maps the data output from the codeword repeater 2608into +1 or −1. A Walsh cover generator 2614 outputs a Walsh cover forsector division by receiving a DRC Walsh cover index. A multiplier 2610multiplies the output of the signal point mapper 2609 by the output ofthe Walsh cover generator 2614. A multiplier 2611 orthogonal-spreads theoutput of the multiplier 2610 by multiplying it by a predeterminedorthogonal code W₀ ¹⁶. A switch 2612, under the control of thecontroller, gates the output of the multiplier 2611. A gain controller2613, gain-controls the output of the switch 2612. A summer 2615 sums upthe outputs of the gain controllers 2606 and 2613.

A bit repeater 2616 repeats ACK (acknowledge) channel data apredetermined number of times. A signal point mapper 2617 maps the dataoutput from the bit repeater 2616 into +1 or −1. A multiplier 2618orthogonal-spreads the signal output from the signal point mapper 2617by multiplying it by a predetermined orthogonal code. A gain controller2619, gain-controls the output of the multiplier 2618.

An encoder 2620 encodes input traffic data, and a channel interleaver2621 interleaves the output of the channel encoder 2620. An interleavedpacket repeater 2622 repeats the interleaved packet data output from thechannel interleaver 2621 a predetermined number of times. A signal pointmapper 2623 maps the data output from the interleaved packet repeater2622 into +1 or −1. A multiplier 2624 orthogonal-spreads the signaloutput from the signal point mapper 2623 by multiplying it by apredetermined orthogonal code. W₂ ⁴ A gain controller 2625 controls again of the signal output from the multiplier 2624. A summer 2626 sumsup the outputs of the gain controllers 2619 and 2625. An HPSK modulator2627 performs HSPK modulation the outputs of the summers 2615 and 2626.A filter 2628 baseband-filters the output of the HPSK modulator 2627.The filtered signal is converted to an RF signal byfrequency-up-conversion and then transmitted to the access network.

FIG. 26 illustrates a structure of a forward link transmitter accordingto an embodiment of the present invention. The transmitter is comprisedof a traffic channel transmitter, a preamble transmitter, a MAC channeltransmitter and a pilot channel transmitter.

First, with regard to the traffic channel transmitter, an encoder 2701encodes forward traffic channel data. For example, a convolutionalencoder or a turbo encoder having a code rate R=⅓ or ⅕ is typically usedfor the encoder 2701. A scrambling code generator 2702 generates ascrambling code for scrambling the traffic data, and a scrambler 2703scrambles the output of the encoder 2701 by XORing it with the output ofthe scrambling code generator 2702. A channel interleaver 2704interleaves the output of the scrambler 2703. A modulator 2705 modulatesthe output of the channel interleaver 2704 and outputs an interleavedsymbol. The modulator 2705 serves as a QPSK (Quadrature Phase ShiftKeying) modulator, an 8-PSK (8-Phase Shift Keying) modulator or a 16-QAM(16-Quadrature Amplitude Modulation) modulator. A symbol repeater 2706repeats the output of the modulator 2705 a predetermined number oftimes. A symbol demultiplexer (DEMUX) 2707 demultiplexes the output ofthe symbol repeater 2706 to N available Walsh code channels. A 16-aryWalsh cover generator 2708 orthogonal-spreads the N outputs of thesymbol demultiplexer 2707. A Walsh channel gain controller 2709gain-controls the outputs of the 16-ary Walsh cover generator 2708. AWalsh chip level summer 2710 sums up the outputs of the Walsh channelgain controller 2709 on a chip level. Various signal information(slotting rate information, repetition frequency information, slottingstart point information, pilot offset information and MAC ID(identification)) and user data mentioned herein are transmitted to theaccess terminal through the traffic channel transmitter. That is, thesignaling message defined herein is transmitted through the trafficchannel transmitter.

Next, regarding the preamble transmitter, a signal point mapper 2711maps preamble data of all 0's to +1 or −1. A multiplier 2712orthogonal-spreads the output of the signal point mapper 2711 bymultiplying it by a specific 64-ary biorthogonal Walsh code (orsequence) associated with a user's unit MAC ID (or MAC index).

Next, regarding the MAC channel transmitter, a signal point mapper 2713maps 1-bit RPC (Reverse Power Control) information to +1 or −1. A PRCWalsh channel gain controller 2714 gain-controls the output of thesignal point mapper 2713. A multiplier 2715 orthogonal-spreads theoutput of the PRC Walsh channel gain controller 2714 by multiplying itby a predetermined orthogonal code associated with the user's unique MACID. A bit repeater 2716 repeats 1-bit RAB information predeterminedtimes. A signal point mapper 2717 maps the output of the bit repeater2716 to +1 or −1. A multiplier 2718 orthogonal-spreads the output of thesignal point mapper 2717 by multiplying it by a predetermined orthogonalcode. A Walsh chip level summer 2719 sumps up the outputs of themultipliers 2715 and 2718 on a chip level. A sequence repeater 2720repeats the sequence output from the Walsh chip level summer 2719 apredetermined number of times.

Next, with regard to the pilot channel transmitter, a signal pointmapper 2721 maps pilot channel data of all 0's to +1 or −1. A multiplier2722 orthogonal-spreads the output of the signal point mapper 2721 bymultiplying it by a predetermined Walsh code.

A time division multiplexer (TDM) 2729 time-division-multiplexes theoutputs of the traffic channel transmitter, the preamble transmitter,the MAC channel transmitter and the pilot channel transmitter accordingto a predetermined rule. A quadrature spreader 2723 complex-spreads theoutput of the time division multiplexer 2729 by multiplying it by agiven PN code. Baseband filters 2724 and 2725 baseband-filter theI-component signal and the Q-component signal output from the quadraturespreader 2723, respectively. For RF modulation, modulators 2726 and 2727multiply the outputs of their associated baseband filters 2724 and 2725by a carrier signal. A summer 2728 sums up the outputs of the modulators2726 and 2727, and forwards the modulated signal to the access terminalthrough an antenna.

FIG. 27 illustrates a procedure for determining the access terminal forreceiving the forward channel and the data rate, described withreference to FIG. 28. Referring to FIG. 27, the access network receivesthe DRC channel transmitted from the access terminal in step 2901, anddetects DRC information by demodulating the received DRC channel in step2903. The access network decides whether to immediately apply thereceived DRC information to the forward channel in step 2904. If theaccess network determined to immediately apply the received DRCinformation to the forward channel, the access network determines theaccess terminal for receiving the forward channel and the data rateusing the received DRC information in step 2907. Otherwise, the accessnetwork stores the detected DRC information to use it when making adecision related to the forward channel later, in step 2905. Afterdetermining the access terminal for receiving the forward channel andthe data rate, the access network transmits data to the determinedaccess terminal at the determined data rate in step 2909.

For a better understanding of the invention, reference will be madeseparately to a transmission operation and a reception operation of theaccess terminal.

The access terminal determines a forward, data rate by measuringstrength of the forward pilot channel, creates DRC information includingthe determined data rate and then transmits the created DRC informationto the access network. Based on the DRC repetition frequency DRCLength(=1, 2 or 4) and the slotted DRC transmission mode DRCSlotMode (=enabledor disabled) previously specified by the access network, the accessterminal transmits new DRC information at every slot (DRCLength=1);creates DRC information at every two slots and transmits the created DRCinformation at one of the 2 slots (DRCLength=2); or creates the DRCinformation at every 4 slots and transmits the created DRC informationat one of the 4 slots (DRCLength=4). That is, for DRCLength=1, theaccess terminal newly measures the reception power of the pilot channelat every slot, determines the forward data rate, and then transmits thecorresponding DRC information to the access network; for DRCLength=2,the access terminal newly measures the reception power of the pilotchannel at every 2 slots, determines the forward data rate, and thentransmits the corresponding DRC information to the access network; andfor DRCLength=4, the access terminal newly measures the reception powerof the pilot channel at every 4 slots, determines the forward data rate,and then transmits the corresponding DRC information to the accessnetwork.

After transmitting the DRC information to the access network, the accessterminal must repeatedly determine for a predetermined time periodwhether the access network transmits forward data at the data ratespecified in the transmitted DRC information. The predetermined timeperiod is variable depending on how long the access network will use thereceived DRC information when selecting the access terminal to which theforward data is to be transmitted. If the access network has previouslyinformed the access terminal of the time interval where it uses the DRCinformation in selecting the forward data rate and the access terminal,using the signaling message, the access terminal is not required todetermine whether the forward data corresponding to the transmitted DRCinformation is received, at every slot until before transmission of thenext DRC information. That is, since the access terminal knows how longthe access network efficiently uses the transmitted DRC information, theaccess terminal can stop receiving the forward data using the signalinginformation from the access network. If the access network has notinformed the access terminal of the time interval where it uses the DRCinformation, the access terminal must check the forward data channel atevery slot until generating the next DRC information after reporting theDRC information to the access network.

FIG. 28 illustrates the valid time intervals where the access terminalreceives the forward traffic channel in response to the transmitted DRCinformation. In the first case, the valid time interval becomes one slotafter the DRC information is transmitted. Therefore, the access terminaldetermines whether the forward traffic data is received, only forone-slot period after transmitting the DRC information, and stops thereceiving operation if it fails to receive the forward traffic in thisperiod. After transmitting the DRC information in the next DRCtransmission period, the access terminal repeats the following process.

FIG. 29 illustrates a procedure for transmitting the DRC information anddetecting forward traffic in the access terminal according to anembodiment of the present invention. Referring to FIG. 29, the accessterminal measures reception power of the forward pilot channel in step3001. Thereafter, the access terminal determines a forward data ratebased on the measured reception power of the pilot channel in step 3003and creates DRC information corresponding to the determined data rate instep 3005. Subsequently, the access terminal transmits the created DRCinformation to the access network over the reverse DRC channel in step3007. After transmitting the DRC information, the access terminaldetermines in step 3009 whether forward traffic data is received fromthe access network. If the forward traffic data is received at therequested data rate, the access terminal receives the forward trafficdata in step 3015. However, upon failure to receive the forward trafficdata, the access terminal determines in step 3011 whether the validinterval of the DRC information has expired. If the valid interval ofthe DRC information has not expired in the access network, the accessterminal returns to step 3009 to determine whether the forward data isreceived at the next slot. However, if the valid DRC informationinterval has expired in the access network, the access terminaldetermines in step 3013 whether the time elapsed after transmission ofthe DRC information is longer than the DRC transmission periodDRCLength. In this process, the access terminal can either repeat orstop reception of the forward channel. If the time elapsed is longerthan the transmission period, the access terminal returns to step 3001,to measure the reception power of the forward pilot channel again andthen perform the succeeding steps. It is assumed herein that the accessnetwork reports the valid DRC information interval to the accessterminal through the signaling message. If the valid intervalinformation is not provided to the access terminal, the step 3011 mustbe canceled.

To sum up, in the slotted DRC transmission mode and the repeated DRCtransmission mode, when the capacity of the reverse link is saturateddue to DRC interference between the users, the access terminals gatetransmission of the DRC channels at predetermined periods, or repeatedlytransmits the same DRC channels at the reduced transmission power,thereby contributing to a reduction in interference between users and anincrease in capacity of the reverse link.

As described above, the slotted DRC transmission method and the repeatedDRC transmission method according to the present invention can resolvethe capacity reduction problem of the reverse link, which may happen inthe HDR system. In the invention, if the capacity of the reverse link issaturated, the access terminal switches to the slotted DRC transmissionmode or the repeated DRC transmission mode. The slotted DRC transmissionmode can contribute to a reduction in interference between the users andan increase in capacity of the reverse link, and the repeated DRCtransmission mode can also contribute to a reduction in interference dueto the DRC channels in the reverse link, thus increasing the capacity ofthe reverse link.

In the above-stated embodiments, the access terminal measures forwardchannel environment(pilot channel) and on the basis of which, reverslytransmits the maximum forward DRC information which the access terminalmay receive. However, the access terminal may transmit the receiptsignal measurement value of forward pilot signal, that is, pilot signalC/I. The invention can also be applied to another case where the accessterminal transmits pilot signal C/I. In this case, the access terminaltransmits the value measuring receipt strength of forward pilot signalaccording to information which can analogize a C/I update period(corresponding to DRC_Length) or other slot rate instructed from thecontroller.

While the invention has been shown and described with reference to acertain preferred embodiment thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. An access network apparatus in a high data rate mobile communicationsystem, comprising: a measuring part for measuring reception power of areverse DRC (Data Rate Control) channel; a controller for determining aslotting rate of the reverse DRC channel by comparing the measuredreception power of the reverse DRC channel with a plurality ofpredetermined threshold values; and a channel transmitter fortransmitting a signaling message including information indicating thedetermined slotting rate to an access terminal.
 2. The access networkapparatus as claimed in claim 1, wherein the signaling message furtherincludes information on a slot where transmitting the reverse DRCchannel is started, and information on whether an offset is applied to apilot channel.
 3. The access network apparatus as claimed in claim 1,wherein the reception power of the reverse DRC channel is defined as anaverage signal-to-noise ratio determined by measuring a signal-to-noiseratio of each reverse DRC channel received from every user and thendividing the measured signal-to-noise ratios by a number of the users.4. The access network apparatus as claimed in claim 1, wherein thereception power of the reverse DRC channel is defined as a least valueof a plurality signal-to-noise ratios measured for reverse DRC channelsreceived from every user.
 5. The access network apparatus as claimed inclaim 1, wherein the signaling message further includes MAC ID (MediumAccess Control Identification).
 6. The access network apparatus asclaimed in claim 5, wherein the access terminal determines a slot wheretransmitting the reverse DRC channel is started, and whether an offsetis applied to a pilot channel, using the slotting rate and MAC IDincluded in the signaling message.
 7. An access network apparatus in ahigh data rate mobile communication system, comprising: a measuring partfor measuring reception power of a reverse DRC channel; a controller fordetermining a repetition frequency (DRCLength) of said reverse DRCchannel by comparing the measured reception power of the DRC channelwith a plurality of predetermined threshold values, and adjustingtransmission power of the reverse DRC channel below transmission powerof a reverse pilot channel; and a channel transmitter for transmitting asignaling message including information indicating the repetitionfrequency and information indicating the transmission power of thereverse DRC channel.
 8. The access network apparatus as claimed in claim7, wherein the signaling message further comprises informationindicating whether the reverse DRC channel is slotted.
 9. An accessnetwork apparatus as claimed in claim 7, wherein a transmission power ofthe DRC channel is determined by multiplying a transmission power of thepilot channel by a reciprocal of the DRC channel repetition frequency.10. A method for transmitting DRC information selected by an accessterminal to an access network in a mobile communication system in whichthe access terminal transmits to the access network DRC informationindicating a selected one of forward data rates requested by the accessterminal, and the access network specifies DRC information lengthindicating a number of slots where the DRC information is repeated andtransmits the DRC information length to the access terminal, wherein theaccess terminal gates transmission of the DRC information to the accessnetwork at one time slot in every DRC information length.
 11. A datatransmission method for an access network in a mobile communicationsystem in which an access terminal transmits to the access network,during call setup, DRC information length indicating a frequency ofrepeating DRC information designating one of several requested forwarddata rates at a plurality of time slots, and the access network receivesthe designated DRC information at the determined one time slot accordingto the DRC information length, wherein upon receipt of the designatedDRC information at the time slot, the access network transmitstransmission data to the access terminal during the designated data rateat the time slots corresponding to the DRC informationlength(DRC_length).
 12. A communication method in a mobile communicationsystem in which an access terminal transmits to an access network DRCinformation indicating a selected one of forward data rates requested bythe access terminal, comprising the steps of: designating a DRCinformation length DRCLength indicating a number of slots where the DRCinformation is repeated and transmitting the designated DRC informationlength from the access network to the access terminal; and gatingtransmission of DRC information to the access terminal at one time slotin every DRC information length received from the access network.
 13. Amethod for determining a access network mode in a mobile communicationsystem in which a continuous mode which continuously transmits data ratecontrol information indicating one of a plurality of forward datatransmission rates at every slot and a gated mode which is gated andtransmitted to one of a predetermined slot are supported, comprising:switching from the continuous mode to the slotted mode if a receiptstrength of a reverse data rate control channel is lower than a firstreference value; switching from the slotted mode to the continuous modeif the receipt strength of the reverse data rate control channel ishigher than a second reference value; and transmitting a signalingmessage including information designating the switched slotted orcontinuous mode to the access terminal.
 14. A method for determining anaccess network mode as claimed in claim 13, wherein the first referencevalue differs from the second reference value.
 15. A method fordetermining a forward data rate of an access network in a mobilecommunication system in which users are grouped into a plurality of usergroups, each user group transmits a DRC information at a time slot inslot period having a predetermined length and the access networkreceives the DRC information, wherein the access network gathers themost recently received DRC information as to each user group anddetermines the forward data rate in a certain time in the slot period.16. A method for transmitting a receipt strength(C/I) informationselected by an access terminal to an access network in a mobilecommunication system in which the access terminal measures a receiptstrength of a forward pilot signal of the access network and transmitsthe receipt strength of the forward pilot signal to the access network,and the access network specifies C/I information length indicating anumber of slots where the C/I information is repeated and transmits theC/I information length to the access terminal, wherein the accessterminal gates transmission of the DRC information to the access networkat one time slot in every DRC information length.